The Trinil fossil femoral sample has played an important, although controversial role in discussions of the early hominin postcranial skeleton since discovery of the first specimen (Femur I) by Dubois in 1892. Here we report the results of new computed tomographic analyses of femoral shaft structure in Femora I-V from Trinil. Femora were scanned using a GE Lightspeed OX/I scanner, with a resulting voxel size of .39 x .39 x .6 mm. A semi-automatic threshold-based segmentation process with manual corrections was used to separate fossilized bone from any matrix; cortical contours were clearly visible at all levels. The resulting data were used to create virtual 3-D representations of all specimens, from which cross-sectional geometric properties (areas, second moments of area) and morphometric maps were derived. Comparisons were carried out with other Early and Middle Pleistocene Homo femora as well as a sample of modern humans.

Although somewhat variable, Trinil Femora II-V exhibit key characteristics shared with other H. erectus femora, including increased mediolateral to anteroposterior bending rigidity in the midshaft and proximal shaft regions, and, in most specimens, relatively thick medial and lateral cortices in the distal shaft. Both of these characteristics are indicative of relatively increased mediolateral bending of the diaphysis, which is consistent with differences in hip structure (e.g., a relatively long femoral neck) associated with Early to Middle Pleistocene Homo. Femur I does not show this pattern, adding to evidence that it is not H. erectus, but rather derives from a more recent time period.

Funding for this study was provided by the French MNHN and the Human Evolution Research Fund at the UI Foundation.